In the film "New York Stories" theres an artist, based loosely, I believe on Chuck Connelly, who paints in this huge studio (that features a basketball court) while using a garbage pail lid for a palette. The depiction is so over the top that it's hard to take it seriously, but after watching a documentary on the artist, it seems a little more plausible. After all, the function of a palette is to hold paint while you put it on the canvas, so I guess if you're working monumentally large, why not a trash can lid?
         In the book I have on the painter Sorolla it shows him holding a palette that's about the size of a small coffee table. Since the brushes he's holding are about two feet long maybe the palette has to match. I would expect him to have had a severe case of tennis elbow. How can you hold a palette that large for any significant amount of time? Most of my palettes average around 16" by 20", some round and some square. After a day of painting I have an incised welt around my thumb, and my arm is killing me. And I work out; push-ups rowing machine, weights, etc;. I can't see myself using a palette any larger than I do right now without needing corrective surgery down the line.
       Some artists favor a rolling table top as a palette. Usually a piece of glass with a neutrally colored paper underneath it. Edward Minoff features a unique approach on his website, he has a Munsell neutral value scale underneath his palette. He uses Munsell's paint chips quite extensively in his working process. Eventually I could see him painting Munsell value stripes on the walls of his studio. I've tried the table palette approach and I didn't like it. I felt a disconnect between my impulse and the hesitation to find the color note on the palette. To use a musical analogy, it would be like playing the violin and laying it down after each note. Flowus interruptus. It was killing my flow.
       I think it was Velasquez who occasionally would use the edge of a canvas as a palette. Usually for small studies. The paint would be mixed from the piles at the bottom of the painting. I saw on Chris Puglieses web site that he has been playing around with this idea with some interesting results. It's neat to watch the little piles get mixed into values that find their way onto the forms. On Tony Ryder's studio blog theres a picture of one of his student's palettes where Tony has done a demo showing how to conceptualize the eye as a storefront window. If that was my palette I would have put it aside and gotten a new one or at the very least, made a transfer rubbing of the image. Not to sell it or anything, but just because it's one of those unique things that artists occasionally do that highlights the transformative powers of art.
      In videos and pictures I've seen of Steven Assael's demos he has his palette clamped vertically to his easel. I guess that makes it a lot easier to see his mixing process. I don't know what kind of paint he uses, but if I tried that, I'm pretty sure my paint would slowly start to slime it's way down the side and eventually onto the floor. It seems that the more expensive the paint is, the more likely it will have some oil separation, because it has less of those binding fillers and stabilizers. I remember showing up to paint at one class where the other students were amazed at my palette because I had half inch mounds of dried color underneath each fresh pile. I explained that I only scraped off the color after it would begin to dry. It didn't make sense to throw away paint that for some colors, might stay usable for a week. I would only clean and wipe down the mixing area. Nelson Shanks takes this idea to the extreme. His dried piles are inches high. I know I need a new palette when I experience "dead arm" after a day of painting.
       It's said that when Whistler gave painting instruction he would critique his student's work by looking at their palettes, not their paintings. Probably apocryphal, but still it highlights the importance some artists place on that miniature stage where the preliminary battle takes place.(sorry for the mixed metaphor). When Matisse was asked to comment on the young upstart Picasso who was challenging his pre-eminence, his comment was that he was good but that he "has no palette". Whew! I can't think of a worse insult. But I'd have to agree with that assessment. Matisse certainly had a palette, no doubt about it. Whatever one may feel about his modernist flourishes, the man certainly knew his colors.
       In "Classical Painting Atelier" the author talks about the difference between a closed palette and an open one. Basically one uses pre- mixed color strings (closed) and the other is mix with your brush as you go (open). When I'm painting still lifes I do a lot of premixing. I l.ike to plan out my strategy and I want my colors placed cleanly and confidantly. When I'm painting out of doors I use the brush mixing system. There just isn't time to mix color strings while you're trying to capture a fleeting light effect while fighting off insects, wayward ducks and tourists. I have to admit that I do enjoy the challenge of it. It is a little more improvisational and often features happy little accidents that find their way back into studio practices.
     One of my instructors encouraged me to hold the palette up vertically near my face as I rushed to the canvas to  apply paint. That way the distance between palette and canvas would be even less. I already suffer from "painters allergies" and I'm sure that if I tried using that technicque that my wife would find me one day passed out on the floor of my studio with paint smeared all over my face. That reminds me of another weird artist movie "Vincent and Theo" which shows Van Gogh with his face alongside his palette eating paint and sipping turpentine. Talk about being "one with your instrument". Lucian Freud has a self portrait (unfortunately nude) that shows the aged artist holding his palette, kind of tipped down, but not dropped to the floor. His knarled up thumb hanging on. I imagine that eventually my fingers will become arthritic from years of being abused by my palette, but I can't ever really see myself painting without one. For me the palette is really the heart and soul of what I do.